1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a photoresist pattern defining an opening having a small critical dimension. The invention also relates to a semiconductor device prepared by the aforementioned method.
2. Description of the Related Art
Semiconductor manufacturing processes have become more complicated, and the integration degree of a semiconductor chip has increased to more than 1 Giga bit DRAM. It has therefore become necessary to form minute patterns according to a design rule of less than 0.25 .mu.m. These minute patterns have recently been formed using a deep-UV (248 nm) light, which has a shorter wavelength than conventional g-line (436 nm) and i-line (365 nm) light, as a light source in the semiconductor manufacturing processes. In addition, half-tone phase shift masks now are being used as the photomask in semiconductor manufacturing processes instead of the conventional light-shielding pattern masks, such as binary chrome masks. The conventional light sources having longer wavelengths (e.g., g-line or i-line) or photoresist materials that are used for the binary chrome mask typically exhibit a low contrast when they are used in a photolithography process, which uses the deep-UV light source and the half-tone phase shift mask. It has therefore not been heretofore possible to form a photoresist pattern defining an opening having a small critical dimension (i.e., small size) to have a desired profile.
In another method for forming a minute pattern, the size of the opening defined by the photoresist pattern can be reduced by thermally flowing the photoresist pattern after forming it. In this thermal flowing method, care should be taken to minimize the variation of the critical dimension (i.e., size, diameter, circumference, etc.) of the photoresist pattern according to changes in temperature. In particular, care should be taken to minimize the variation of the critical dimension due to differences of flow rates according to the shape and position of the opening. Accordingly, photoresists suitable for use in this thermal flowing method are those whose flow rate, i.e., flow amount per unit temperature (nm/.degree. C.), is small such that the flow rate can be easily controlled. Conventional photoresists, however, exhibit a high flow rate (nm/.degree. C.) so that controlling the flow rate of the photoresist is difficult.